Conventionally, there have been roughly two types of fin attachment structures for surfboards, namely a fixed fin type, and a detachable fin type.
As compared to the fixed fin type the detachable fin type is used more frequently and there are various attachment structures because it allows the attachment of a fin in an arbitrary shape according to a user's preference. In addition, the fin can be detached and carried.
That is, an embedded fin box and the like are pre-arranged on the bottom surface of a surfboard. The fin is then detachably mounted in the fin box.
One prior disclosure of screw fixing as structures that allow a fin to be detachable when the fin is broken or carried include those disclosed in Japanese Unexamined Patent Publication (Kokai) No. H6-255575 (patent document 1), Translated Japanese Publication of Patent Application No. 2001-520961 (patent document 2), Translated Japanese Publication of Patent Application No. 2002-530242 (patent document 3), and Japanese Unexamined Patent Publication (Kokai) No. 2003-306195 (patent document 4).
These prior disclosures have a structure in which screws, bolts or the like are used to fasten a fin for fixing the fin to the fin box.
In addition to the above, structures in which grooves having various structures are provided in the fin box and the fin is fastened by fitting the fin into a groove include those disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2005-74026 (patent document 5), Japanese Unexamined Patent Publication (Kokai) No. 2005-112206 (patent document 6), and Japanese Unexamined Patent Publication (Kokai) No. 2006-280839 (patent document 7).
Furthermore, a structure in which the fin is fastened using a C-shaped clamp, there is disclosed in Translated Japanese Publication of Patent Application No. 2003-528003 (patent document 8).
Structures in which the fin is fastened so that it can be attached detachably using a special locking member include those disclosed in Translated Japanese Publication of Patent Application No. 2005-508798 (patent document 9) and Translated Japanese Publication of Patent Application No. 2005-526664 (patent document 10).
Furthermore, a structure in which both the fin box and the fin fitted therein have a fitting structure in a special shape such that the fin is fastened detachably, is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2007-160969 (patent document 11).    Patent document 1: Japanese Unexamined Patent Publication No. H6-255575    Patent document 2: Translated Japanese Publication of Patent Application No. 2001-520961    Patent document 3: Translated Japanese Publication of Patent Application No. 2002-530242    Patent document 4: Japanese Unexamined Patent Publication (Kokai) No. 2003-306195    Patent document 5: Japanese Unexamined Patent Publication (Kokai) No. 2005-74026    Patent document 6: Japanese Unexamined Patent Publication (Kokai) No. 2005-112206    Patent document 7: Japanese Unexamined Patent Publication (Kokai) No. 2006-280839    Patent document 8: Translated Japanese Publication of Patent Application No. 2003-528003    Patent document 9: Translated Japanese Publication of Patent Application No. 2005-508798    Patent document 10: Translated Japanese Publication of Patent Application No. 2005-526664    Patent document 11: Japanese Unexamined Patent Publication (Kokai) No. 2007-160969
As described above, there exist various attachment structures for attaching a fin of a surfboard.
For example, the structure disclosed in Japanese Unexamined Patent Publication No. H6-255575 adopts so-called screw fixing, in which a screw is tightened to fix the fin, or the fin can be detached by unscrewing the screw.
Because of this, attachment and detachment of the fin require a special tool, such as a screwdriver.
Furthermore, for example, when the fin comes into contact with human in use, the fin will remain fastened and human body may be injured. That is, it is unlikely that the fin will separate from the board to prevent the fin from injuring the human in such an emergency.
Next, in the structures disclosed in Japanese Publication of Patent Application No. 2001-520961, Japanese Publication of Patent Application No. 2002-530242, and Japanese Unexamined Patent Publication (Kokai) No. 2003-306195, a fin is fastened by screws in a transverse direction. Detachment of the fin similarly requires a special tool such as a screwdriver. Thus, for example, even if the surfer falls during surfing and the fin of the surfboard comes into contact with a human body, the fin will remain fastened to the board. There is thus a possibility that the fin may inure the human body.
Further, the structures shown in Japanese Unexamined Patent Publication (Kokai) No. 2005-74026 and Japanese Unexamined Patent Publication (Kokai) No. 2005-112206 are those in which a fin is inserted along a groove and fastened to a predetermined position. The fin can be tightly attached, thus being difficult to separate from the board.
That is, while the structure is not classified as the group of structures which rely on screw fixing of the fin, the fin is nonetheless tightly inserted in the recess portion in order to prevent the fin from dislodging unnecessarily when in use and fixed in place in the groove.
As a result, the fin is tightly fitted thereto in order to prevent its dislodgement. Thus, it is unlikely that the fin readily comes off the board just by the impact of a collision or the like, e.g., with a human body.
That is, under this impact, the fin comes off only when the impact is applied in a particular specific direction. However, even if the impact is from the direction in which the fin comes off, the fin just moves a small amount and will stop after such movement. As a result, the damage to the human body from the fin at the time of contact cannot be prevented.
The fin disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2006-280839 is similarly inserted into the groove, and moved along the groove to be attached.
In this case, it is necessary to attach or detach the fin in accordance with the insertion procedure. For an unexpected impact, however, the fin is unlikely to come off when in use as long as the fin does not suffer an impact in a specified direction.
Consequently, when the fin comes into contact with human body, there is a high possibility that the fin remains attached to the board causing injury to the human body.
In the configuration shown in Japanese Publication of Patent Application No. 2003-528003, a C-shaped clamp is used to fasten the fin to the fin box as a locking member. That is, the fin is tightly fitted to the clamp in a so-called fin box. A large force is required to detach the fin and at the same time, it is difficult to detach the fin unless the fin is pulled out in a given direction relative to the fin box.
Consequently, an impact that is applied when the fin comes into contact with a human body during surfboard use or an impact in a certain direction will not cause the fin to come off. Therefore the fin remains fastened to the surfboard.
Furthermore, there arises another need, such that the accuracy at the time of attachment is required. That is, at least the slot must be matched or the fin must be inserted tightly into the clamp.
According to Japanese Publication of Patent Application No. 2005-508798, a cam is rotated by the worm gears in order to fix the fin to the surfboard. Therefore, the rotation of the worm gears is necessary for attaching/detaching the fin. The fin is thus fastened to the board and is unlikely to separate from the board by impact when in use.
Consequently, it is not possible to dislodge the fin in an emergency.
Japanese Publication of Patent Application No. 2005-526664 discloses a tag pin that is placed in a pin slot and tightened by a club screw. The fin is thus fastened tightly thereto, but the fin is unlikely to be dislodged and separate from the board in an emergency.
Furthermore, according to Japanese Unexamined Patent Publication (Kokai) No. 2007-160969, the fin can be attached easily, but its attachment is done by inserting the fin in an obliquely backward direction. If a screw is not used to fix the fin, there is a possibility that the fin comes off only when a force is applied from a given direction in an emergency.
Consequently, when the fin comes into contact with a human body from a variety of unexpected directions, that is, when the fin comes into contact with a human body during use of the surfboard, the fin remains almost in the fixed state. Therefore, contact with human body without the possibility of injury cannot be achieved.
As described above, a certain fin attachment structure is desired, which causes the fin to readily come off so as to prevent injury to a human body, that is, which causes the fin to come off the surfboard in a safe manner when in use.
Furthermore, it is originally required for the fin to be attached tightly to the surfboard without abruptly coming off other than in an emergency such as at the time of contact.
Still furthermore, as shown in the prior art, the attachment structure needs to be of a type in which the fin can be attached/detached readily for replacement and is fastened securely to the surfboard.
In addition, when the fin is attached to the board, there will inevitably be a space between the fin and the groove of the board.
That is, if this space is eliminated, at the time of attachment/detachment of the fin, the fin is rubbed throughout the entire groove, thus being hard to be attached or detached.
Therefore, although there inevitably exits a little space, at the time of being attached, this space will cause the fin to rattle.
In the case of the repetition of the attachment/detachment, or in the case of the use of an arbitrary fin with respect to a board based on the preference of a user, or the like, this space inevitably becomes larger. Such a problem must also be properly dealt with.
In particular, as well as regarding a fin that is readily detachable, also regarding a fin to be screwed and fixed, the rattle that may occur between the fin and the groove may cause instability at the time of take-off during normal usage. This fin rattle may further result in the reduction of operability. Some solutions to this problem are thus needed.
Conventionally, either paper or vinyl is forced into the space between the fin and the groove as a filler, or a gum tape or a cloth tape is wound around the fin to fill the space, these methods actually in practice result in a larger space. Additionally it can be difficult to attach or detach the fin by use of such fillers.
Thus, some methods as a solution to such problems have been desired.